This is a sketch of a python3 script that checks git tag written in a modified semantic version format and returns a C file with the parsed version code and the git hash

gittag2C.py

#!/usr/bin/env python3
# This script checks git tag written in a modified semantic version format
# and returns a C file with the parsed version code and the git hash
# The git tag MUST conform to this format v<major>.<minor>.<patch>-<rcX>

import subprocess
import sys, os
import re

tagname = subprocess.check_output(["git", "describe", "--tags"]).strip().decode("utf-8") ;
tagnamelong = subprocess.check_output(["git", "describe", "--tags", "--long"]).strip().decode("utf-8") ;
shorthash = subprocess.check_output(["git", "rev-parse", "--short", "HEAD"]).strip().decode("utf-8") ;

################################################################################
# Constants

MAGIC_NUMBER = "0x43505300";
HEADER_VERSION = 0;
HEADER_LENGTH = 1024;
FW_LENGTH = 896*1024;
VENDOR_NAME = "VENDOR_NAME";
FW_NAME = "APP";

################################################################################
# Based on https://github.com/python-semver/python-semver/blob/master/semver.py
# format: v<major>.<minor>.<patch>-<rc.X> e.g. v0.0.1-rc13 or v0.0.1-rc.13
_REGEX = re.compile(
        r"""
        ^
        v
        (?P<major>(?:0|[1-9][0-9]*))
        \.
        (?P<minor>(?:0|[1-9][0-9]*))
        \.
        (?P<patch>(?:0|[1-9][0-9]*))
        (\-(?P<prerelease>
            (?:0|[1-9A-Za-z-][0-9A-Za-z-]*)
            (\.(?:0|[1-9A-Za-z-][0-9A-Za-z-]*))*
        ))?
        (\+(?P<build>
            [0-9A-Za-z-]+
            (\.[0-9A-Za-z-]+)*
        ))?
        $
        """, re.VERBOSE)

match = _REGEX.match(tagname);

if match is None:
  print(f"git tag is not valid semantic version: {tagname}");
  sys.exit(os.EX_USAGE); # Failed

# Version
version_parts      = match.groupdict();
VERSION_MAJOR      = version_parts["major"]; # Required
VERSION_MINOR      = version_parts["minor"]; # Required
VERSION_PATCH      = version_parts["patch"]; # Required
VERSION_PRERELEASE = 0;                      # Optional

if version_parts["prerelease"] != None:
  release_candidate = re.search('rc\.?([0-9]+)', version_parts["prerelease"], re.IGNORECASE)
  if release_candidate:
    VERSION_PRERELEASE = release_candidate.group(1)

VERSION_BUILD      = shorthash;

################################################################################

if VERSION_PRERELEASE == 0:
  SEM_VER_PRINT = f"{VERSION_MAJOR}.{VERSION_MINOR}.{VERSION_PATCH}+{VERSION_BUILD}";
else:
  SEM_VER_PRINT = f"{VERSION_MAJOR}.{VERSION_MINOR}.{VERSION_PATCH}-rc{VERSION_PRERELEASE}+{VERSION_BUILD}";

c_source = f"""\
/*
  Autogenerated Firmware Header

  `git describe --tags --long` --> {tagnamelong}
  `git rev-parse --short HEAD` --> {shorthash}

  Version (https://semver.org/ Semantic Versioning 2.0.0):
    {SEM_VER_PRINT}
*/

fw_header_t __attribute__((section(".firmware_header")))
running_firmware_header = {{
  .magic              = {MAGIC_NUMBER}
  .hdrver             = {HEADER_VERSION},
  .hdrlen             = {HEADER_LENGTH},
  .applen             = {FW_LENGTH},
  .name               = "{FW_NAME}",
  .version_major      = {VERSION_MAJOR},
  .version_minor      = {VERSION_MINOR},
  .version_patch      = {VERSION_PATCH},
  .version_prerelease = {VERSION_PRERELEASE},
  .version_build      = "{VERSION_BUILD}"
}};
"""

print(c_source);
sys.exit(os.EX_OK); # Completed

Example output:

/*
  Autogenerated Firmware Header

  `git describe --tags --long` --> v0.0.1-0-g5bf2243
  `git rev-parse --short HEAD` --> 5bf2243

  Version (https://semver.org/ Semantic Versioning 2.0.0):
    0.0.1+5bf2243
*/

fw_header_t __attribute__((section(".firmware_header")))
running_firmware_header = {
  .magic              = 0x43505300
  .hdrver             = 0,
  .hdrlen             = 1024,
  .applen             = 917504,
  .name               = "APP",
  .version_major      = 0,
  .version_minor      = 0,
  .version_patch      = 1,
  .version_prerelease = 0,
  .version_build      = "5bf2243"
};